This invention pertains to carbonaceous refractory compositions, particularly such compositions suited for pressing into brick shape.
It is known to form a refractory brick by pressing a composition of refractory aggregate (for example, refractory periclase grain) combined with a pitch bond which may also contain other carbonaceous materials, such as carbon black, graphite, and the like. In order to form a pressed brick which has adequate strength to be handled and shipped without slumping or breaking, it is customary to use a bonding pitch with a high (for example, 110.degree. C.) softening point. This means that the brick must be formed (pressed) with a hot aggregate/pitch mixture which, when it cools, hardens to form a strong, coherent brick.
In recent years, for various reasons, for example, to avoid working with hot pitch mixtures, it has become the practice to use a synthetic resin, for example a phenol formaldehyde resin, as bond. These resins can be used in liquid form at room temperature to form the brick and are then set by heating at temperatures of, for example, 110.degree. to 300.degree. C. to form strong, hard, refractory shapes.
These products are placed in service without firing at elevated temperatures, although they may be tempered at temperatures up to 500.degree. C. and, in rare instances, coked at temperatures up to 1000.degree. C. When placed in service in a furnace which is raised to an elevated temperature, the carbonaceous materials in the brick coke, forming a carbon bond.
When a synthetic resin bond was substituted for the tar or pitch bond in refractories containing graphite, it was found that the substitution led to low density, high porosity, and lowered strength in the brick. In other words, the bonding of the grains by the matrix was generally poorer when the resin was substituted directly for the pitch in prior compositions.
The present invention is directed to the solution of this problem. In other words, the present invention permits the forming of resin-bonded, graphite-containing refractory compositions into brick which have as high density and strength, and as low porosity, as the former tar or pitch-bonded refractories containing graphite. In addition, the invention has further application in that it also improves the properties of graphitic refractory brick bonded with a natural resin, such as coal tar pitch.